I have both, and my F77 blows the New Model M out of the water in so many ways. It has significantly higher build quality, better materials, better keycaps, and it is nicer to type on. The new model M from Unicomp isn't terrible, but it's made out of plastic, has some creak/flex to it, less crisp legends, slightly less pleasant key feel, and just generally looks and feels cheaper in every way possible. But that's because it is cheaper, and the board it's modeled after was cheaper. As far as approximating what they are attempting to reproduce, they both do a good job, although I would say the F77 is better.
color blind test (https://colorblind-test.io)
I have both, and my F77 blows the New Model M out of the water in so many ways. It has significantly higher build quality, better materials, better keycaps, and it is nicer to type on. The new model M from Unicomp isn't terrible, but it's made out of plastic, has some creak/flex to it, less crisp legends, slightly less pleasant key feel, and just generally looks and feels cheaper in every way possible. But that's because it is cheaper, and the board it's modeled after was cheaper. As far as approximating what they are attempting to reproduce, they both do a good job, although I would say the F77 is better.
color blind test (https://colorblind-test.io)
F > M. That's not even up for debate. ;D Some people may prefer the sound and weighting of an M, not sure why anybody would prefer for them to be less consistent (if it needs a bolt/screw mod) and less smooth. The M is objectively structurally questionable from the factory. One bad drop and you're popping rivets out of the plate sandwich. Membranes last longer than some might think, but they're not nearly as robust as a capacitive PCB. Its legendary status for durability is illusory.
The question was How different the repros are to the originals though.
Welcome, by the way. Glad you're loving the F77. I hope at least some people in the New Members section aren't getting ghosted. People don't typically ever look there. I haven't put in the effort to respond to them en masse for some time.